U2's Bono and Edge amazed fans at a charity gig in north London last night with a surprise appearance.

The 250-strong crowd at the Mencap Little Noises Sessions at Union Chapel had been told to expect "very special guests", but were stunned by Bono and Edge's 20-minute acoustic set.

BBC Radio1 DJ Jo Whiley introduced the duo as a warm-up act for Biffy Clyro - who were performing at the gig alongside We Are Scientists and the Courteneers – and described them as an up-and-coming band.

"Please welcome Edge and Bono," she elaborated.

Bono and Edge then played Stay, Desire, Angel of Harlem and Wave of Sorrow.

"Our Christmas song," said Bono on Angel of Harlem, while he explained that Wave of Sorrow – never before performed live – had finally been 'finished' after making its first appearance on Joshua Tree B-sides 20 years ago.

"Don't tell [U2 bandmates] Larry [Mullen] and Adam [Clayton] about this," Bono continued, despite the fact that Clayton was actually at the gig.

24/11/2007 12:34:40